pushing shoulder back to make shorter cartridge

i was thinking about a wildcat based off 7 rum necked down to .257 but with the shoulder pushed back and haveing longer neck with a case overall length of about a 30-06. if i were to get a custom die for these dimentions, would a full length sizing die work for this? would it end up crushing the case or would it push the shoulder back like i wanted and just trim the neck to length? would it work with a sharp 35 or 40 degree angle? if not, how would i go about pushing the shoulder back to shorten up the case?

i was thinking about a wildcat based off 7 rum necked down to .257 but with the shoulder pushed back and haveing longer neck with a case overall length of about a 30-06. if i were to get a custom die for these dimentions, would a full length sizing die work for this? would it end up crushing the case or would it push the shoulder back like i wanted and just trim the neck to length? would it work with a sharp 35 or 40 degree angle? if not, how would i go about pushing the shoulder back to shorten up the case?

it's going to take a lot of press to get there for starters (and I mean a lot). My suggestion is for you to make up a series of form dies, and start with a .300 RUM case instead of a 7mm. Reason is that it will be a lot easier I doubt the die will allow this much of a setback in one push, so I'd suggest you push the shoulder back rougly .25", and cut the case off with a jewler's saw. Then push it down to about 2.56" total length. I'll assume you plan on keeping the 30 degree sholder angle, so at least that part will be easier. You'll probably want to make up a couple of forming dies out of something like A2, and harden them to about 58-62RC. Plus a final sizing die off the chamber reamer (you really need two reamers here; one for the chamber and another to ream the die blank). The final form die could be a bushing die that would allow you to work the case down in steps (.315", .295", and finally .287 [you may end up making a bushing]). The hard part is creating a false shoulder to get everything in the right place, and you can plan on annealing the necks at least once in the middle of the process. To be honest with you, it would almost be easier to start out with a .338 RUM case, and push the shoulder back. Then do it with a 7mm, and do the final push with the right size your after. I see a lot of work, and even more ruined cases just getting there. Think you'd be better off making a .257 Weatherby. The RUM case will be way overbore, and barrel life will not be good at all. But if this is what you want, I'd advise you to anneal the necks and shoulders of the case before you even start. Then plan on doing it again about half way thru the process (necks and a small part of the shoulder) because the brass is really going to work harden. I'd also guess you'll have more money in forming dies and loading dies than you will in the rest of the build.
gary

i was thinking about a wildcat based off 7 rum necked down to .257 but with the shoulder pushed back and haveing longer neck with a case overall length of about a 30-06. if i were to get a custom die for these dimentions, would a full length sizing die work for this? would it end up crushing the case or would it push the shoulder back like i wanted and just trim the neck to length? would it work with a sharp 35 or 40 degree angle? if not, how would i go about pushing the shoulder back to shorten up the case?

forming a 35 or 40 degree shoulder will cause you a lot of grief with this case!! Suggest you "Goggle 30 Meyer" to give you a rough idea about creating the shoulders
gary